1. Field of the Invention
The present invention relates to a three-axis attitude control propulsion device as a part of a five-axis attitude control propulsion device used in a flying object. The device of the present invention is specifically suitable for use in a flying object such as an artificial satellite, on-trajectory work station, lunar probe, planet probe, aerospace craft, launching rocket, etc.
2. Description of the Prior Art
A flying object is known that flies or cruises while its attitude is being controlled by a propulsion device performing a five-axis attitude control. The propulsion device in this case is a prime mover that obtains a thrust as a reaction upon an action to jet outside a high pressure fluid, especially a high temperature and high pressure gas. As a typical one of the propulsion devices, a rocket engine is known.
In the flying object of the above-mentioned type, the attitude control or proceeding direction control is carried out by the propulsion device performing the five-axis control in total of a two-axis translational control and a three-axis attitude control.
The two-axis translational control will be described for reference. Where an entire part of a flying object having a certain magnitude is considered a material particle, the two-axis translational control has two axes for performing a space motion control of the flying object. Supposing that the material particle is proceeding by inertia in the direction of the X axis in a three dimensional space, a trajectory of the flying object can be changed by a thrust being added in the directions of the remaining two axes, that is, the Y axis and the Z axis. These are called the two-axes of the translational control.
Nevertheless, the actual flying object has a certain magnitude and also has a shape other than a spherical shape. Hence, even if an imaginary material particle, that is, a position of the center of gravity, is identical in a flying object, the flying object can take various different attitudes. There are three freedoms of attitude, that is, a pitch, roll and yaw. These are called three axes of the attitude control.
As prior art in this field, Japanese Patent 3,291,542 is known, wherein there are provided five pairs of nozzles, that is, ten pieces of nozzles, each pair having two nozzles directed reversely to each other, so that thrusts are generated in a maximum of ten directions to thereby perform the five-axis control, that is, the two-axis translational control and the three-axis attitude control.
In this prior art, there is provided a nozzle plug in each of the pairs of nozzles and operation of the nozzle plug can be selected such that an entire quantity of combustion gas is jetted from one of the nozzles or a half quantity of combustion gas is jetted from each of the nozzles. For this selection, a two-way discharge changeover means is used and this means is provided in each of the five pairs of nozzles.
Out of the ten nozzles, four nozzles of two pairs are used for the two-axis translational control. The remaining six nozzles of three pairs are used for the three-axis attitude control. But, as the four nozzles of the two pairs used for the two-axis translational control do not directly relate to the three-axis attitude control propulsion device of the present invention, description thereof will be omitted. Hence, description of the prior art here will proceeded on the basis of the device having six nozzles of three pairs.
In this kind of technology, however, even if no thrust is wanted to be generated in a specific direction, a mode is employed such that a half quantity of the combustion gas is jetted from each of the two nozzles of a corresponding pair to thereby cancel the thrust. Thus, the efficiency of use of the combustion gas is reduced and there arises a disadvantage that a surplus of propellant as a combustion gas source must be loaded or, if a loading quantity of the propellant is limited, an operable time of the three-axis attitude control propulsion device is reduced or an obtainable thrust is reduced. It is to be noted that the situation of jetting the combustion gas by this technology will be described later as the “Comparison Example” in comparison with embodiments according to the present invention.
Separately from the above technology, a construction having six nozzles is also known in which the six nozzles are individually opened and closed by six valves. According to this construction, while a waste of the propellant can be suppressed, the number of valves to be operated increases and the structure of the device becomes complicated to thereby easily invite a weight increase. That is, while an advantage is obtained on one side, a disadvantage is also caused on the other side.
Also, in the technology disclosed by the above-mentioned Japanese Patent 3,291,542, the nozzle plug as a flow passage selecting means is of a reciprocating type and it directly receives pressure of the high temperature high pressure combustion gas. For this reason, in the mode that the entire quantity of the combustion gas flows to one nozzle, the nozzle plug continuously receives the pressure of the combustion gas in the direction to maintain that state and a stable condition can be obtained. However, if the mode is to be changed over to another mode, that is, to a mode in which the half quantity of the combustion gas flows to the opposite nozzle or to a mode in which the entire quantity of the combustion gas flows to the opposite nozzle, there is a need to use a drive means having a large operating torque sufficient to overcome the pressure of the combustion gas. This leads to a disadvantage in that the weight of the three-axis attitude control propulsion device increases.